High precision dc voltage regulator



Dec. 31, 1968 .1. R. GATELY 3,419,789

HIGH PRECISION DC VOLTAGE REGULATOR Filed April 19, 1966 8 l5 \l8 INPUT LINE 9 VOLTAGE J I2 REGULATED OUTPUT 20 3 :0 l3 l4 l6 FIG I. PRIOR ART 4 P T 5 IN U 3 I LINE 0 2 VOLTAGE AK REGULATED l 20 OUTPUT 2 FIG. 2

FIG-3 FIG. 4

INVENTOR.

JOSEPH R. GATELY ATTORNEY United States Patent 3,419,789 HIGH PRECISION DC VOLTAGE REGULATOR Joseph R. Gately, Woodside, N.Y., assignor to Forbro Design Corp., New York, N.Y., a corporation of New York Filed Apr. 9, 1966, Ser. No. 543,707 Claims. (Cl. 323-22) ABSTRACT OF THE DISCLOSURE The present invention concerns voltage regulating circuits and, in particular, a high precision DC voltage regulator suitable for use :as a reference voltage source and the like.

Zener diodes are widely used as voltage regulating devices utilizing their well known characteristic of avalanche breakdown wherein at some predetermined reverse bias voltage such diodes conduct and exhibit a relatively low impedance. If the impedance of the conduction region were zero, it would have no slope and the voltage across the diode would be constant regardless of the current passed. However, Zener diodes have a finite conduction resistance and hence, to utilize them for precise voltage references, the current is kept as constant as possible. Another characteristic of Zener diodes which make them less than ideal is their voltage/temperature coetficient. Temperature compensated Zener diodes have been developed comprising two back-to-back connected Zener diodes wherein the negative temperature coefiicient of the forward conducting or temperature compensating diode off-sets the positive temperature coeflicient of the reverse or Zener connected diode and in which these oppositely directed temperature ellects are matched at a predetermined or rated current. These temperature compensated diodes require not only a constant current for constant voltage but a particular constant current for minimum temperature coeflicient as well. The present invention is concerned with improvements in temperature compensated Zener regulated voltage circuits.

Accordingly, one object of the present invention is to provide improved voltage regulating characteristics in temperature compensated Zener diode circuits.

Another object is to provide methods of and means for utilizing temperature compensated Zener diodes in a circuit having improved voltage regulating characteristics.

These and other objects of the present invention will be apparent from the detailed description of the invention given in connection with the various figures of the drawing.

In the drawing:

FIGURE 1 is a circuit diagram of a prior art concept of a Zener diode regulator.

FIGURE 2 is a circuit diagram of a Zener diode regulator in accordance with the present invention.

FIGURE 3 is an alternate starting circuit suitable for use in the circuit of FIGURE 2 shown only as a detail.

FIGURE 4 is another alternate starting circuit suitable for use in the circuit of FIGURE 2 shown only as a detail.

FIGURE 1 showing a prior art circuit diagram shows a regulating circuit utilizing a line voltage input transformer including a primary 1 for connecting to a source of alternating current line voltage, a core 2, and a secondary 3 providing suitable voltage to a rectifier network including rectifiers 4, 5, 6 and 7 which in turn charge capacitor 8 to a suitable DC voltage for use in powering the 3,419,789 Patented Dec. 31, 1968 balance of the circuit. A first Zener diode 18 to be fed with .a constant current is connected between lines 16 and 17. Constant current to this Zener is provided by the circuit including transistor 11 and second Zener diode 9. Transistor 11 is operated in a constant current mode since current to its emitter 13 is controlled by Zener 9 and emitter resistor 10. The current to emitter 13 is equal to the voltage drop across Zener 9 minus the base to emitter drop of transistor 11 divided by resistance of resistor 10. Current to Zener 9 and base 12 is supplied through resistor 15. Under these conditions the current from collector 14 to Zener 18 will be controlled and equal to th .above described substantially constant emitter current less current to base 12. The voltage across Zener 18 thus regulated by its own avalanche characteristic and the substantially constant current from transistor 11 is applied through fixed resistor 19 to a third Zener diode 20 so that the voltage across Zener 20 is thus doubly regulated and provides the regulated output across lines 16 and 21. Since the voltages across Zener 18 and 20 are substantially constant, the current to Zener 20 is constant and equal to the difference between the voltages across these Zeners divided by the resistance of resistor 19.

While this prior art circuit provides a well regulated output voltage, it has some limitations. The voltage applied to resistor 15 and Zener 9 varies as the power line voltage varies and hence the current to Zener 9 varies and this variation results in a slight change in the voltage regulated by Zener 9. This in turn causes a slight variation in the current from transistor 11 to Zener 18 and there is a slight variation in the regulalted voltage across Zener 18. This again causes a slight variation in current to the final Zener 20 and results in less than perfect regulation of the regulated output voltage across lines 16 and 21. This whole chain of events is particularly enhanced by the use of temperature compensated Zeners 18 and 20 which have a higher regulating impedance than non-compensated Zeners. Also- Zener 9 is not temperature compensated in order to provide a lower regulating impedance for its function. So we have in this prior art circuit some effect of line voltage and temperature on the regulated output voltage.

The circuit of FIGURE 2 provides a method of and means overcoming the limitations of the prior art circuit as described above. Since certain portions of the circuit of FIGURE 2 function in a similar manner to corresponding portions of FIGURE 1, the corresponding circuit elements in the two circuits are designated by the same numbers. In FIGURE 2 an additional constant current transistor circuit is provided utilizing transistor 24 which regulates the current to Zener 22. The circuit of transistor 24 includes Zener 31 connected between base 27 and line 17, emitter current determining resistor 28 connected between line 17 and emitter 26 and resistor 23 connected between col lector 25 and the junction between one end of Zener 22 and base 12 of transistor 11. The current supplied to Zener 22 is controlled in a similar manner to the controlled current functioning of transistor 11 as described above. The current to emitter 26 is equal to the Zener voltage of Zener 31 less the base to emitter voltage of transistor 24 divided by the resistance of resistor 28. This controlled current is fed to Zener 22. Resistor 23 is provided merely to lessen the voltage drop across transistor 24. The first regulation between lines 16 and 17 is provided by the two temperature compensated Zeners 31 and 32 connected in series. The second stage of regulation is supplied by current determining resistor 19 and Zener 20 to provide the final highly regulated voltage across lines 16 and 21.

With the constant current supply to Zener 22, line voltage variations effects on the current to Zener 22 are greatly reduced providing an improved constancy of regulated voltage across Zener 22 and with this constant current the higher impedance but temperature compensated Zener may be used as Zener 22. In this way improved regulating characteristics in the presence of line voltage variations is obtained and at the same time improved temperature characteristics are provided. The circuit also provides the critical operating current required for minimum temperature coefficient of the temperature compensated Zener 22.

It will be seen that Zener 31 and transistor 24 provide controlled current to Zener 22 while Zener 22 and transistor 11 supply controlled current in turn to Zener 31. This interdependent circuit may not start unless a starting current is provided to Zener 22. This may be accomplished by connecting a resistor 29 between base 27 and collector 25. This resistor should be of a high enough resistance value to draw a current which is small compared with the normal current controlled by transistor 24 in order not to degrade its control.

Restating the mode of operation of the circuit of FIG- URE 2, unregulated DC voltage is first produced across capacitor 8, as described above in connection with FIG- URE 1. When line voltage is first applied, the larger part of the DC voltage across capacitor 8 appears across resistor 29, since it is of high enough resistance value to draw a current small compared with the normal current controlled by transistor 24. This high voltage between base 27 and collector 25 starts conduction in transistor 24 and the current in Zener diode 31 builds up until transistor 24 is regulating and passing rated current to transistor 11 and hence to Zener diode 22 which in turn starts to regulate the-current of transistor 11. At this point transistor 24 is regulating the current in Zener 22 and transistor 11 is regulating the current in Zener diodes 31 and 32. This reciprocal action greatly reduces the effects of line voltage on the regulated voltage across Zener diodes 31 and 32 and permits the use of temperature compensated Zener diodes with improved regulation and temperature coefficient. The regulated voltage across Zener diodes 31 and 32 is applied through high stability resistor 19 to the final voltage regulating Zener diode across which the regulated output voltage is taken.

FIGURES 3 and 4 show alternate starting circuits. Capacitor 33 connected between base 27 and collector will supply a starting surge if the line voltage is suddenly applied to the circuit and will carry no degrading current under steady state operating conditions. Another starting circuit utilizes Zener diode 34 connected between base 27 and collector 25. The Zener breakdown voltage of Zener 34 should be greater than the normal operating drop across transistor 24 but less than the turn-on surge voltage. In this way the circuit will be started but the Zener 34 will draw no degrading current during steady state operation of the regulator circuit.

While one form of the present invention has been shown and described together with some minor modifications, many modifications will be apparent to those skilled in the art and within the spirit and scope of the invention as set forth particularly in the appended claims.

What is claimed is:

1. In a voltage regulating circuit, the combination of;

a source of voltage to be regulated (8) including a first side and a second side first and second transistors each including a base, an

emitter and a collector wherein said transistors are complimentary types;

a first Zener diode connected between said first side of said voltage source and the base (12) of said first transistor (11) for establishing a first predetermined voltage therebetween;

a first resistor connected between said first side of said voltage source and the emitter (13) of said first transistor for determining the emitter current in accordance with said first predetermined voltage;

a second Zener diode connected between said second side of said voltage source and the base (27) of said second transistor for establishing a second predetermined voltage therebetween;

a second resistor connected between said second side of said voltage source and the emitter (26) of said second transistor for determining the emitter current in accordance with said second predetermined voltage;

conductive means connected between the collector (25) of said second transistor (24) and the base (12) of said first transistor (11);

a third Zener diode (32) connected between the collector (14) of said first transistor and said second Zener diode (31);

a series circuit comprising a resistor (19) and a fourth Zener diode (20) shunted across the said second and third Zener diodes (31 and 32);

whereby said first transistor (11) and first Zener diode (22) provide regulated current to said second and third Zener diodes in series and said second transistor (24) and second Zener diode (31) provide regulated current to said first Zener diode (22) and said fourth Zener diode (20) provides a regulated output voltage thereacross.

2. A voltage regulating circuit as set forth in claim 1 and including;

a resistor connected across said second transistor for providing a starting current in the said second Zener diode (31).

3. A voltage regulating circuit as set forth in claim 1 and including;

a capacitor connected between the base (27) and collector (25) of said second transistor for providing a starting current in the said second Zener diode (31).

4. A voltage regulating circuit as set forth in claim 1 and including;

a fifth Zener diode (34) connected between the base (27) and collector (25) of said second transistor for providing a starting current in the said second Zener diode (31).

5. A voltage regulating circuit as set forth in claim 1 and wherein;

said first, second, third and fourth Zener diodes are back-to-back connected temperature compensated Zener diodes.

References Cited UNITED STATES PATENTS 3,007,102 10/1961 Kennedy 32116 3,022,457 2/1962 Doan 323-22 3,031,608 4/1962 Von Eschen et al 323-22 JOHN F. COUCH, Primary Examiner.

A. D. PELLINEN, Assistant Examiner.

U.S. Cl. X.R. 

